While high molecular weight copolymerization polyesters have been acknowledged of their usefulness and are used in the above-mentioned fields of utilization, particularly in the fields requiring superior flexibility and superior adhesion to various substrates, they are mostly used upon dissolution in an organic solvent.
There are already known many methods for making low molecular weight copolymerization polyesters dispersible or soluble in aqueous media by graft polymerization. For example, U.S. Pat. No. 3,634,351, 4,517,322 and Japanese Patent Publication No. 57065/1982 disclose such techniques. flowever, the target polyesters in these references are alkyd resins having very low molecular weights and a film obtained from an aqueous dispersion of such a polyester has inferior processability and poor water resistance.
The methods for making high molecular weight copolymerization polyesters dispersible or soluble in aqueous media are disclosed in Japanese Patent Publication No. 57874/1986 and Japanese Patent Unexamined Publication Nos. 223374/1984, 225510/1987 and 294322/1991. Yet, those methods are industrially disadvantageous in that a crosslinking reaction causing gelation occurs as a side reaction, only reactions and uses at low solid concentrations are attainable, procedures are complicated due to the steps to introduce a double bond into terminal of copolymerization polyester, reactions are hard to control, productivity is low and or the like.
In view of the situation as described, the present invention aims at forming, without adding an emulsifier, an aqueous dispersion of fine polyester particles permitting good re-dispersibility by dispersing the particles in water or an aqueous solvent with a sufficiently low content of an organic solvent, which dispersion being stable even at high solid concentrations, as well as providing an aqueous dispersion of a graft-polymerized polyester satisfying extremely high levels of processability and adhesion to a substrate as those possessed by a raw material polyester and preventing gelation caused by crosslinking reaction.